Mammalian mitogen-activated protein (MAP)1 kinases are serine/threonine kinases that mediate intracellular signal transduction pathways (Cobb and Goldsmith, 1995, J Biol. Chem., 270, 14843; Davis, 1995, Mol. Reprod. Dev. 42, 459). Members of the MAP kinase family share sequence similarity and conserved structural domains, and include the ERK2 (extracellular signal regulated kinase), JNK (Jun N-terminal kinase), and p38 kinases. JNKs and p38 kinases are activated in response to the pro-inflammatory cytokines TNF-alpha and interleukin-1, and by cellular stress such as heat shock, hyperosmolarity, ultraviolet radiation, lipopolysaccharides and inhibitors of protein synthesis (Derijard et al., 1994, Cell 76, 1025; Han et al., 1994, Science 265, 808; Raingeaud et al., 1995, J Biol. Chem. 270, 7420; Shapiro and Dinarello, 1995, Proc. Natl. Acad. Sci. USA 92, 12230). In contrast, ERKs are activated by mitogens and growth factors (Bokemeyer et al. 1996, Kidney Int. 49, 1187).
ERK2 is a widely distributed protein kinase that achieves maximum activity when both Thr183 and Tyr185 are phosphorylated by the upstream MAP kinase kinase, MEK1 (Anderson et al., 1990, Nature 343, 651; Crews et al., 1992, Science 258, 478). Upon activation, ERK2 phosphorylates many regulatory proteins, including the protein kinases Rsk90 (Bjorbaek et al., 1995, J. Biol. Chem. 270, 18848) and MAPKAP2 (Rouse et al., 1994, Cell 78, 1027), and transcription factors such as ATF2 (Raingeaud et al., 1996, Mol. Cell Biol. 16, 1247), Elk-1 (Raingeaud et al. 1996), c-Fos (Chen et al., 1993 Proc. Natl. Acad. Sci. USA 90, 10952), and c-Myc (Oliver et al., 1995, Proc. Soc. Exp. Biol. Med. 210, 162). ERK2 is also a downstream target of the Ras/Raf dependent pathways (Moodie et al., 1993, Science 260, 1658) and may help relay the signals from these potentially oncogenic proteins. ERK2 has been shown to play a role in the negative growth control of breast cancer cells (Frey and Mulder, 1997, Cancer Res. 57, 628) and hyperexpression of ERK2 in human breast cancer has been reported (Sivaraman et al., 1997, J Clin. Invest. 99, 1478). Activated ERK2 has also been implicated in the proliferation of endothelin-stimulated airway smooth muscle cells, suggesting a role for this kinase in asthma (Whelchel et al., 1997, Am. J. Respir. Cell Mol. Biol. 16, 589).
Aurora-2 is a serine/threonine protein kinase that has been implicated in human cancer, such as colon, breast and other solid tumors. This kinase is believed to be involved in protein phosphorylation events that regulate the cell cycle. Specifically, Aurora-2-may play a role in controlling the accurate segregation of chromosomes during mitosis. Misregulation of the cell cycle can lead to cellular proliferation and other abnormalities. In human colon cancer tissue, the aurora-2 protein has been found to be overexpressed. See Bischoff et al., EMBO J., 1998, 17, 3052–3065; Schumacher et al., J. Cell Biol., 1998, 143, 1635–1646; Kimura et al., J. Biol. Chem., 1997, 272, 13766–13771.
Glycogen synthase kinase-3 (GSK-3) is a serine/threonine protein kinase comprised of α and β isoforms that are each encoded by distinct genes [Coghlan et al., Chemistry & Biology, 7, 793–803 (2000); Kim and Kimmel, Curr. Opinion Genetics Dev., 10, 508–514 (2000)]. GSK-3 has been implicated in various diseases including diabetes, Alzheimer's disease, CNS disorders such as manic depressive disorder and neurodegenerative diseases, and cardiomyocete hypertrophy [WO 99/65897; WO 00/38675; and Haq et al., J. Cell Biol. (2000) 151, 117]. These diseases may be caused by, or result in, the abnormal operation of certain cell signaling pathways in which GSK-3 plays a role. GSK-3 has been found to phosphorylate and modulate the activity of a number of regulatory proteins. These proteins include glycogen synthase which is the rate limiting enzyme necessary for glycogen synthesis, the microtubule associated protein Tau, the gene transcription factor β-catenin, the translation initiation factor e1F2B, as well as ATP citrate lyase, axin, heat shock factor-1, c-Jun, c-Myc, c-Myb, CREB, and CEPBα. These diverse protein targets implicate GSK-3 in many aspects of cellular metabolism, proliferation, differentiation and development.
In a GSK-3 mediated pathway that is relevant for the treatment of type II diabetes, insulin-induced signaling leads to cellular glucose uptake and glycogen synthesis. Along this pathway, GSK-3 is a negative regulator of the insulin-induced signal. Normally, the presence of insulin causes inhibition of GSK-3 mediated phosphorylation and deactivation of glycogen synthase. The inhibition of GSK-3 leads to increased glycogen synthesis and glucose uptake [Klein et al., PNAS, 93, 8455–9 (1996); Cross et al., Biochem. J., 303, 21–26 (1994); Cohen, Biochem. Soc. Trans., 21, 555–567 (1993); Massillon et al., Biochem J. 299, 123–128 (1994)]. However, in a diabetic patient where the insulin response is impaired, glycogen synthesis and glucose uptake fail to increase despite the presence of relatively high blood levels of insulin. This leads to abnormally high blood levels of glucose with acute and long term effects that may ultimately result in cardiovascular disease, renal failure and blindness. In such patients, the normal insulin-induced inhibition of GSK-3 fails to occur. It has also been reported that in patients with type II diabetes, GSK-3 is overexpressed [WO 00/38675]. Therapeutic inhibitors of GSK-3 therefore are considered to be useful for treating diabetic patients suffering from an impaired response to insulin.
GSK-3 activity has also been associated with Alzheimer's disease. This disease is characterized by the well-known β-amyloid peptide and the formation of intracellular neurofibrillary tangles. The neurofibrillary tangles contain hyperphosphorylated Tau protein where Tau is phosphorylated on abnormal sites. GSK-3 has been shown to phosphorylate these abnormal sites in cell and animal models. Furthermore, inhibition of GSK-3 has been shown to prevent hyperphosphorylation of Tau in cells [Lovestone et al., Current Biology 4, 1077–86 (1994); Brownlees et al., Neuroreport 8, 3251–55 (1997)]. Therefore, it is believed that GSK-3 activity may promote generation of the neurofibrillary tangles and the progression of Alzheimer's disease.
Another substrate of GSK-3 is β-catenin which is degradated after phosphorylation by GSK-3. Reduced levels of β-catenin have been reported in schizophrenic patients and have also been associated with other diseases related to increase in neuronal cell death [Zhong et al., Nature, 395, 698–702 (1998); Takashima et al., PNAS, 90, 7789–93 (1993); Pei et al., J. Neuropathol. Exp, 56, 70–78 (1997)].
As a result of the biological importance of GSK-3, there is current interest in therapeutically effective GSK-3 inhibitors. Small molecules that inhibit GSK-3 have recently been reported [WO 99/65897 (Chiron) and WO 00/38675 (SmithKline Beecham)].
Aryl substituted pyrroles are known in the literature. In particular, tri-aryl pyrroles (U.S. Pat. No. 5,837,719) have been described as having glucagon antagonist activity. 1,5-Diarylpyrazoles have been described as p38 inhibitors (WO 9958523).
There is a high unmet medical need to develop new therapeutic treatments that are useful in treating the various conditions associated with ERK2 activation. For many of these conditions the currently available treatment options are inadequate.
Accordingly, there is great interest in new and effective inhibitors of protein kinase, including ERK2 inhibitors, that are useful in treating various conditions associated with protein kinase activation.